Getting a fake burger to taste like the real thing is no mean feat. Food scientists can grow meat from small sets of cultured animal cells with increasing success, but the high cost is rather unpalatable. Cheaper plant-based alternatives, to some, might be even more so. The Impossible Burger brings a meaty flavor to its plant-sourced patties with one key, and controversial, ingredient, which has just been recognized as safe by the US Food and Drug Administration (FDA).

What makes meat meat? For Impossible Foods, creator of the Impossible Burger, it's all about a molecule called heme. That distinctly meaty taste? Heme. The bloody texture? Heme. That sizzle, that aroma and those resulting cravings? It's all heme, baby.

Heme can be found in the human body, where it grabs oxygen from our lungs and carries it around our bloodstream, also creating its distinct red coloring. And it can be found in great abundance in animal muscle, which is what makes real burgers so tasty, according to Impossible Foods.

And conveniently for its scientists, an identical, atom-for-atom version can be found in the root modules of soy plants. Impossible Foods takes the DNA from these modules and adds it to its own genetically engineered yeast, which is then fermented to produce a heme protein called soy hemoglobin that carries the heme molecule. It is then mixed with other typical meat substitutes like wheat protein, potato protein and soy protein to produce a beef-like patty with a bloody residue, but is a whole lot more environmentally friendly.

According to the company, producing the Impossible Burger involves 75 percent less water, 87 percent less greenhouse gases and 95 percent less land than traditional beef patties. Its stated mission is to reduce the monumental environmental impact of the meat industry.

But not all environmentalists were overjoyed with this creation. In 2014 Impossible Foods voluntarily submitted the science of its burger to the FDA for approval under its Generally Recognized as Safe (GRAS) rules. The agency had some questions and requested more data, particularly around its potential as an allergen, although at the same time didn't declare it unsafe. This left Impossible Foods free to go on selling the burger in thousands of restaurants across the US, including the likes of White Castle and Umami Burger.

This fence-sitting unsurprisingly drew the ire of environmental groups who were concerned about introducing a new genetically engineered additive into the food chain, and called for the Impossible Burger to be pulled from menus. Impossible Foods then carried out more testing, including studies on rats and comprehensive analysis of allergen databases, providing the data it gathered to the FDA in a 1,066-page submission. The FDA has now responded with what is known as a no-questions letter, meaning that it accepts the view that the food is indeed safe to eat.

In some ways nothing changes for Impossible Foods, which was able to keep selling the burger anyway. But getting a clean bill of health from regulators is certainly a boon from a PR point of view for a young company with grand objectives – and indeed the "clean meat" movement as a whole.

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